ForHosting KIT · Developer Utilities

Coherence time calculator

The coherence time calculator converts a light source's coherence length into the time interval over which its electromagnetic field remains predictably related to itself.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Enter a positive coherence length in metres, and the calculator divides it by the exact speed of light in vacuum. The response reports seconds, picoseconds, and femtoseconds, making the result practical for laser measurements, interferometry, spectroscopy, and optical system design without requiring a manual scientific-notation conversion.

What coherence time describes

Coherence time is a temporal measure of how long the phase relationship of light remains useful for interference. A source with a longer coherence time can maintain visible interference when two optical paths differ by a larger travel time, while a source with a short coherence time loses that stable relationship more quickly. This calculator starts from coherence length, the corresponding distance measure, and converts that distance into a vacuum travel time. The relationship is direct because light covers the coherence length during one coherence-time interval. Coherence time is especially useful when comparing lasers, filtered sources, and broadband emitters on a common temporal scale. It does not say how bright a source is, how tightly it is focused, or how long a pulse lasts. Those quantities may interact with a real experiment, but they are not interchangeable with temporal coherence. The result should therefore be read as the time associated with the supplied coherence-length definition, not as a complete description of the source or its noise spectrum.

How the calculation works

The calculation uses the equation coherence time equals coherence length divided by the speed of light in vacuum. The speed is fixed at exactly 299,792,458 metres per second in SI, so the only input is coherence length in metres. For example, a longer length produces a proportionally longer time: doubling the input doubles every reported time value. The primary answer is returned in seconds, while picoseconds and femtoseconds are included because optical coherence intervals are often extremely small. All three fields represent the same duration, merely expressed at different scales. Input must be finite, positive, and no greater than the published calculation limit. Zero and negative distances have no physical meaning for this conversion and are rejected instead of producing a misleading result. The computation performs no lookup and makes no assumption about wavelength, refractive index, spectral shape, or linewidth. If coherence length was measured inside a medium or derived with a convention that uses another propagation speed, first ensure that a vacuum-speed conversion is the intended model.

Using the result in optical work

Use the seconds field when feeding the result into another SI-based formula, and use the picosecond or femtosecond field when communicating laboratory-scale values without long strings of zeros. In an interferometer, the calculated interval can help relate a permissible optical path difference to a travel-time difference. In source comparison, it provides a consistent way to contrast coherence lengths that may span many orders of magnitude. In spectroscopy, it can serve as a starting point for checking whether a reported temporal scale is compatible with the stated coherence distance. Keep significant figures in perspective: the vacuum speed of light is exact, but the coherence length supplied by a measurement usually is not. The output cannot be more experimentally precise than that input. Also verify the definition used by the instrument or reference, because some treatments define coherence width using different correlation thresholds or spectral line-shape conventions. This calculator intentionally applies only the stated distance-over-vacuum-speed relationship, making the numerical operation transparent, reproducible, and easy to audit.

What you can do with it

Plan an interferometer

Convert a source's coherence length into a time scale when assessing optical path-delay tolerances.

Compare light sources

Place lasers, filtered emitters, or broadband sources on the same temporal coherence scale.

Check laboratory calculations

Verify a reported coherence-time conversion and obtain readable picosecond and femtosecond values.

FAQ

What formula does the calculator use?

It uses coherence time = coherence length / 299,792,458 metres per second.

Which unit should I use for coherence length?

Enter coherence length in metres. The result is returned in seconds, picoseconds, and femtoseconds.

Is the speed of light an adjustable input?

No. This capability specifically uses the exact speed of light in vacuum, as required by the stated conversion.

Is coherence time the same as pulse duration?

No. Coherence time describes temporal phase correlation, while pulse duration describes the time extent of a pulse.

How much does the API calculation cost?

Each API request costs $0.002. The browser calculator can run locally without an API request.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/optics/coherence-time

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/optics/coherence-time \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"coherence_length_m":3}'

const res = await fetch("https://api.kit.forhosting.com/optics/coherence-time", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "coherence_length_m": 3
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/optics/coherence-time",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "coherence_length_m": 3
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/optics/coherence-time", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"coherence_length_m":3}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"coherence_length_m":3}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/optics/coherence-time", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "coherence_length_m": 3
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "optics.coherence_time",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

max_coherence_length_m 1000000000000000

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →